This invention relates to a combination weighing method for automatically weighing out batches of product with a predetermined target weight, using a combination weighing machine. In particular, this invention relates to such method improved to be able to use two target weights at the same time.
Among the prior art combination weighing methods, one method involves utilizing a plurality of weighing units each adapted to weigh a fraction of the weight to be delivered and each adapted for unloading of product therefrom to contribute to a delivery. The method comprises for each delivery the steps of generating the values of combinations of weights on the weighing units which were unloaded in the preceding delivery and comparing the values with an acceptable weight standard relating to a predetermined target weight to select a combination of weighing units to be unloaded to deliver a sum weight equal or approximate to the target weight, unloading the weighing units of the selected combination, loading the weighing units which were unloaded, and wherein, for each delivery, the step of generating and comparing the values of the combinations of weights on the weighing units excluding those units which were unloaded on the preceding delivery is initiated before completion of weighing out new loads in those weighing units. An example of this method is disclosed in coassigned U.S. Pat. Nos. 4,385,671 and 4,470,166.
In another prior art method, a plurality of weighing hoppers, each having a weight sensor, is provided. Each weighing hopper is associated with an auxiliary hopper, and an auxiliary hopper memory is provided corresponding to each auxiliary hopper. Product is weighed by each weighing unit and the product weight then transferred to the associated auxiliary hopper memory. The stored values are combined in various fashion to obtain a combination having a weight equal or approximate to a predetermined target weight. An example of such method is disclosed in coassigned U.S. Pat. Nos. 4,437,527 and 4,446,938.
According to the above method of the '671 patent, it is possible to increase the number of deliveries of product per unit time to obtain high speed operation. However, this speed of operation or rate of delivery is naturally limited by the use of a single collection chute for collecting batches of product discharged from selected hoppers, since operation at speeds above a certain limit results in unavoidable intermixture of the successive deliveries of product on the chute. One solution of this problem is disclosed in the opened Japanense patent specification No. 58-2621. In this case, the combination weighing machine includes two collection chutes and is designed to discharge successive deliveries of product"; alternately into either chute.
In practice, it is often required to weigh out the same product using two or more target weights, as where different packages of varying weights are required. In the prior art, however, it is necessary to use two or more combination weighing machines in parallel to accomplish this. If the device of above-cited Japanese specification could deliver product from two collection chutes with different total weight values, it would be effective to execute the required operation.
Accordingly, an object of this invention is to provide an improved method for executing combination computation using two preset target weights to provide two kinds of deliveries of product having different total weights through two collection chutes of such a combination weighing machine as disclosed in the above-cited Japanese patent specification.